Low-pressure gas-discharge lamp for producing resonance radiation

ABSTRACT

A low-pressure gas-discharge lamp for producing resonance radiation comprising two electrodes for a positive column discharge, and at least one cylindrical sputtering electrode coaxially surrounding the column discharge. The sputtering electrode has a step-shaped collar and contains an element whose resonance radiation is desired. Inner and outer insulating tubes on both sides of the sputtering electrode restrict the resonance radiation to space within the sputtering electrode therefore providing a lamp of high intensity and very narrow spectral line profile.

United States Patent Inventors Louis Benjamin Beijer;

Johannes Adrianus Cornelis Jansen, both of Emmasingel, Eindhoven, Netherlands Appl. No. 818,600

Filed Apr. 23, 1969 Patented June 15, 1971 Assignee U. S. Philips Corporation New York, N.Y.

LOW-PRESSURE GAS-DISCHARGE LAMP FOR PRODUCING RESONANCE RADIATION 10 Claims, 1 Drawing Fig.

US. Cl 313/206, 313/207, 313/209 Int. Cl H0lj 61/10 Field of Search 313/206, 207,209, 210; 356/96, 87

[56] References Cited UNITED STATES PATENTS 3,390,297 6/1968 Vollmer 313/209 3,406,308 10/1968 Yamasaki 313/209 X Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorney-Frank R. Trifari ABSTRACT: A low-pressure gas-discharge lamp for producing resonance radiation comprising two electrodes for a positive column discharge, and at least one cylindrical sputtering electrode coaxially surrounding the column discharge. The sputtering electrode has a step-shaped collar and contains an element whose resonance radiation is desired. Inner and outer insulating tubes on both sides of the sputtering electrode restrict the resonance radiation to space within the sputtering electrode therefore providing a lamp of high intensity and very narrow spectral line profile.

DJ ag o PATENTEU JUN1SI971 3585.436

INVENTORS LOUIS B. I JOHANNES E AN SEN AGEM LOW-PRESSURE GAS-DISCHARGE LAMP FOR PRODUCING RESONANCE RADIATION The invention relates to a low-pressure gas-discharge lamp for producing resonance radiation comprising two electrodes between which in operation a positive column discharge is maintained, at least one cylindrical sputtering electrode, which coaxially surrounds the column discharge in operation and which comprises an element whose resonance radiation is desired, furthermore on either side of and coaxially to the sputtering electrode a tube of insulating material, the inner diameter of which is smaller than the inner diameter of the sputtering electrode.

Such lamps are known from Dutch Pat. application No. 6,711,757, laid up for public inspection and are mainly employed in spectrophotometry, particularly in flame spectrometry.

In the known lamps two discharges can be adjusted independently of each other, that is to say, a positive column discharge and a glow discharge on the sputtering electrode, which is held at a negative potential relative to the locally prevailing plasma potential. The ions striking the sputtering electrode will cause sputtering of material from this electrode so that atoms of the element whose resonance radiation is desired are introduced into the positive column. These atoms can be excited by the electrons in the column discharge, after which inter alia they emit their resonance radiation.

The aforesaid known lamps have the advantage that absorption of the resonance radiation emerging along the axis of the column discharge is minimized. The tubes located on either side of the sputtering electrode restrict the atomic vapor to the space inside the sputtering electrode. As a result excitation occurs at all places in the lamp where absorption by the atomic vapor is found. It is thus possible to produce resonance radiation with high intensity and a very narrow spectral line profile.

The invention has for its object to provide an improved construction of such gas-discharge lamps.

A low-pressure gas-discharge lamp of the kind set forth is characterized in accordance with the invention in that each insulating tube is fastened by means of a radially projecting flange to a cylindrical supporting body of insulating material, arranged coaxially to the tube, in that the outer surface of the sputtering electrode is provided with a rotation-symmetrical collar whose sectional area in a plane passing through the axis is steplike and in that the end of the supporting body facing the sputtering electrode bears on the face of the collar which is at right angles to the axis and is at the largest distance from the axis, while the supporting body embraces part of the collar.

A lamp in accordance with the invention comprises a cylindrical supporting body bearing by one end on an external'collar of the sputtering electrode. The tube secured to the supporting body is fixed by the supporting body in the desired position near the end of the sputtering electrode. This construction permits in a very simple manner of stacking up the sputtering electrode with the tubes located at'the ends thereof in the lamp, while mechanical contact between the tubes and the sputtering electrode is avoided. This contact has to be avoided since otherwise material of the tubes may get into the column discharge due to sputtering. The tube is secured to the supporting body by means of a radially projecting flange so that a column discharge along the outer surface of the tube is prevented.

In a lamp in accordance with the invention thecollar arranged on the outer surface of the sputtering electrode has a steplike shape. The end of the supporting body facing the sputtering electrode bears on the face of the step being spaced apart by the largest distance from the axis of the sputtering electrode. In this construction a cylindrical, capillary space is formed between the sputtering electrode and the supporting body. Any material (from the sputtering electrode) deposited on the tube surface and the supporting body is thus prevented from coming into conductive contact with the sputtering electrode. The possibility of the discharge terminating at the tube and the supporting body, which may give rise to sputtering of undesirable material, is then excluded.

In order to restrict the sputtering effect of the column discharge to the inner surface of the sputtering electrode, the tube may be disposed so that one end thereof is located inside the sputtering electrode. According to the invention it is preferred to use a supporting body which surrounds the tube wholly or partly.

The tube and the supporting body may be integral with each other and be made of vitreous quartz. In some cases it is preferred to use sintered alumina as the material for the supporting body and the tube. Sintered alumina has the advantage of greater thermal conductivity than vitreous quartz and may be made with accurate fit in one operation by pressing.

The construction in accordance with the invention may be employed with great advantage in discharge tubes comprising a pluralityof consecutive sputtering electrodes. Two consecutive sputtering electrodes are separated from each other by a common supporting body, inside of which a common tube is fastened. Since it is possible to pile up sputtering electrodes and tubes with the aid of the supporting bodies, a great number of sputtering electrodes may be arranged in a lamp in a cheap, reliable manner. In fact practical manufacture of lamps comprising a plurality of sputtering electrodes not contaminating each other is only possible by the construction in accordance with the invention.

In a low-pressure gas-discharge lamp in accordance with the invention, comprising a lamp envelope and a lamp bottom, a cathode and an anode for the column discharge, the supporting body located near the cathode is preferably constructed so that it can bear on the lamp bottom. The assembly of sputtering electrode(s), tubes and supporting bodies then bears on the lamp bottom. In order to fix this assembly in position on the lamp bottom, it is preferred in accordance with the invention to use one or more current supply wires or stay poles which urge the assembly against the lamp bottom.

In a lamp in accordance with the invention it is advantageous to pass the cathode current supply wires through the interior of the supporting body located near the cathode and to pass the current supply wires for the further electrodes outside said supporting body. In this way undesirable discharges between the current supply wires are avoided.

If the sputtering electrode contains a readily evaporating element, the vapor pressure of this element is likely to become too high at the prevailing temperature of the sputtering electrode. According to the invention this can be obviated by promoting the drainage of heat from the sputtering electrode and/or the tube, for example, by providing parts of the outer surface of the sputtering electrode and, if desired, of the supporting body with cooling vanes. Then the use of sintered alumina as the material for the tube and the supporting body is also advantageous.

The invention will now be described more fully with reference to a drawing which shows schematically a sectional view of a low-pressure gas-discharge lamp in accordance with the invention, which comprises two sputtering electrodes.

The lamp shown in the drawing comprises a glass envelope 1 having a lamp bottom 2 and a vitreous quartz window 3. The discharge space is filled with argon at a pressure of3 mm. Hg. Reference numeral 4 designates a filament cathode coated with electron-emitting material and 5 designates a plateshaped anode having a central aperture. Between the cathode 4 and the anode 5 a positive column discharge is maintained during the operation of the lamp. The lamp comprises two sputtering electrodes 6 and 7 of copper and iron respectively. At the end of the sputtering electrode 6 facing the cathode 4 a vitreous quartz tube 8 is arranged, which has an outer diameter smaller than the inner diameter of the sputtering electrode 6 and which extends inside this electrode 6 over a small distance. The tube 8 is fastened by a radially protruding flange 9 to a vitreous quartz supporting tube 10 so that the column discharge is compulsorily produced in the interior of the tube 8. The supporting body bears by its end 11 facing the electrode 6 on a step-shaped collar 12, arranged on the outer surface of the sputtering electrode 6. The end 11 of the supporting body 10 bears on the face 13 of the step-shaped collar 12 so that at 14 a cylindrical, capillary space is formed between the supporting body 10 and the electrode 6. The end 15 of the supporting body 10 bears on the lamp bottom 2.

The end of the sputtering electrode 7 facing the anode is closed by a vitreous quartz tube 16, which extends partially inside the electrode 7 and is fastened by a flange 17 to a vitreous quartz supporting body 18. The supporting body 18 bears on a collar 19 of the electrode 7 in the same manner as is described for the supporting body 10.

The two sputtering electrodes 6 and 7 are separated from each other by a common vitreous quartz tube 20, which is secured by a flange 21 to a common supporting body 22 of vitreous quartz. The supporting body 22 bears on the stepshaped collars l2 and 19 so that cylindrical, capillary spaces 23 and 24 are formed between the supporting body 22 and the respective electrodes 6 and 7.

The current supply wires 25 and 26 for the cathode 4 are located inside the supporting body 10. The further current supply wires in the lamp are located outside said supporting body and are coated with insulating material. The current supply wires 27 and 28 for the anode 5 clamp by means of this anode the assembly of sputtering electrodes, supporting bodies and tubes against the lamp bottom 2. Reference numeral 29 designates the supply wire for the sputtering electrode 6. The supply wire for the electrode 7 is not visible in the drawing. Reference numeral 30 designates a getter ring. Mica plates 31 prevent the occurrence of undesirable discharges between the electrodes and serve for centering the assembly of sputtering electrodes and supporting bodies.

What we claim is:

l. A low-pressure gas-discharge lamp for producing resonance radiation comprising a hermetically sealed cylindrical envelope having a window at one end, two electrodes for maintaining a positive column discharge, a first insulating tubular structure comprising sections for containing said discharge, at least one cylindrical sputtering electrode comprising an element producing resonance radiation in presence of said discharge, said sputtering electrode interposed between the sections of said first structure for exposure ofsaid discharge to said sputtering electrode, a second insulating tubular structure coaxial to said first structure and comprising sections between edges facing outwardly projecting annular faces of the sputtering electrodes, and cross flanges holding the sections of said first structure to the sections of said second structure to confine resonance radiation within said sputtering electrodes.

2. A low-pressure gas-discharge lamp for producing resonance radiation comprising a hermetically sealed cylindrical envelope having a quartz window at one end, two spaced electrodes for maintaining a positive column discharge along the longitudinal axis of said envelope, at least one hollow cylindrical sputtering electrode comprising an element having desired resonance radiation characteristics for interaction with said column discharge, said sputtering electrode having an axial symmetric, step-shaped outer surface coaxially surrounding said column discharge, inner tubes of insulating material on both sides of said sputtering electrode generally coaxial to said column discharge, the outside diameters of said inner tubes being less than the inside diameter of said sputtering electrode, cylindrical supporting bodies generally coaxial to said inner tubes and having ends bearing on faces of the outer surface of said sputtering electrode orthogonal to and furthest from said column discharge, and radial projecting flanges of insulating material fastened between said inner tubes andsaid supporting bodies to restrict resonance radiation interactions to space within said sputtering electrode.

3. A low-pressure gas-discharge lamp as claimed in claim 2,

wherein one end of the inner tubes is located inside the sputtermg electrode and the supporting body surrounds at least part of the inner tubes.

4. A low-pressure gas-discharge lamp as claimed in claim 2 wherein the inner tubes and the supporting bodies form units of vitreous quartz.

5. A low-pressure gas-discharge lamp as claimed in claim 2 wherein the inner tubes and the supporting bodies form units of sintered alumina.

6. A low-pressure gas-discharge lamp as claimed in claim 2 wherein a plurality of sputtering electrodes are arranged one after the other, and two consecutive sputtering electrodes are separated from each other by common inner tubes and supporting bodies.

7. A low-pressure gas-discharge lamp as claimed in claim 2 wherein outer surfaces of at least one of the sputtering electrodes and of at least one of the supporting bodies are provided with cooling vanes.

8. A low-pressure gas-discharge lamp as claimed in claim 2 wherein the two spaced electrodes for maintaining a positive column discharge includes an anode located near said quartz window and a cathode located near the end of the envelope opposite said window and the supporting body located near the cathode bears on the end of the envelope opposite said quartz window.

9. A low-pressure gas-discharge lamp as claimed in claim 8 further comprising one or more current supply wires and stay poles forcing the anode, the supporting bodies and the sputtering electrodes against the end of the envelope opposite said quartz window.

10. A low-pressure gas-discharge lamp as claimed in claim 8 wherein current supply wires for the cathode are inside the supporting body located near the cathodes and the current supply wires for the further electrodes are outside said supporting body. 

2. A low-pressure gas-discharge lamp for producing resonance radiation comprising a hermetically sealed cylindrical envelope having a quartz window at one end, two spaced electrodes for maintaining a positive column discharge along the longitudinal axis of said envelope, at least one hollow cylindrical sputtering electrode comprising an element having desired resonance radiation characteristics for interaction with said column discharge, said sputtering electrode having an axial symmetric, step-shaped outer surface coaxially surrounding said column discharge, inner tubes of insulating material on both sides of said sputtering electrode generally coaxial to said column discharge, the outside diameters of said inner tubes being less than the inside diameter of said sputtering electrode, cylindrical supporting bodies generally coaxial to said inner tubes and having ends bearing on faces of the outer surface of said sputtering electrode orthogonal to and furthest from said column discharge, and radial projecting flanges of insulating material fastened between said inner tubes and said supporting bodies to restrict resonance radiation interactions to space within said sputtering electrode.
 3. A low-pressure gas-discharge lamp as claimed in claim 2, wherein one end of the inner tubes is located inside the sputtering electrode and the supporting body surrounds at least part of the inner tubes.
 4. A low-pressure gas-discharge lamp as claimed in claim 2 wherein the inner tubes and the supporting bodies form units of vitreous quartz.
 5. A low-pressure gas-discharge lamp as claimed in claim 2 wherein the inner tubes and the supporting bodies form units of sintered alumina.
 6. A low-pressure gas-discharge lamp as claimed in claim 2 wherein a plurality of sputtering electrodes are arranged one after the other, and two consecutive sputtering electrodes are separated from each other by common inner tubes and supporting bodies.
 7. A low-pressure gas-discharge lamp as claimed in claim 2 wherein outer surfaces of at least one of the sputtering electrodes and of at least one of the supporting bodies are provided with cooling vanes.
 8. A low-pressure gas-discharge lamp as claimed in claim 2 wherein the two spaced electrodes for maintaining a positive column discharge includes an anode located near said quartz window and a cathode located near the end of the envelope opposite said window and the supporting body located near the cathode bears on the end of the envelope opposite said quartz window.
 9. A low-pressure gas-discharge lamp as claimed in claim 8 further comprising one or more current supply wires and stay poles forcing the anode, the supporting bodies and the sputtering electrodes against the end of the envelope opposite said quartz window.
 10. A low-pressure gas-discharge lamp as claimed in claim 8 wherein current supply wires for the cathode are inside the supporting body located near the cathodes and the current supply wires for the further electrodes are outside said supporting body. 